Tuesday, October 19, 2010

If you're interested in the phenomenology of quantum gravity...

It's not very technical, so don't hesitate to have a look. It's basically a summary of interesting developments and hopefully explains why I like working in the area. If you're not from the field, you might stumble over one or the other expression, but I think you'll still get a pretty good impression what it's all about.

48 comments:

Thanks for pointing out this new paper of yours and I can assure you, as with others you have written, I will read it with great interest; now as to guaranteeing I will come to understand it is an entirely different matter.

A very good paper, thank you Bee. I actually skim-read it this a.m. because I noticed your tweet re same in the right-hand margin, including: That was much more work than I thought it would be - Bee .

You cover QUITE a bit of territory in but a scant 24 pages, including Supersillystrings theory. Extremely readable and rich, all to the good. Good job. Add 200 pages of anecdotes and you have your first book. :-)

Quantum gravity suffers with the same problem, like string theory, i.e. with the lack of clear fixed postulate list.

The bunch of phenomenological theories, which "has been motivated by LQG, though no rigorous derivation exists to date" is too close to fast growing families of various string theories.

Such phenomenological theories may or may not correspond the quantum gravity theories at all. The main purpose of these theories is just to generate jobs for mathematicians, who would have no better employment.

Zephir, your last sentence reveals a disconnect in your mind between Applied Mathematics and Theoretical Physics. While close, and a great deal of blending exists between them, they are nevertheless different.

So please elaborate because I don't understand what you said. You can bring Experimental Physics and Pure Mathematics, the two bookends, into the discussion as well, but I don't see the need, atm.

Glad you like it. I don't think though at this point the topic would make for a good pop sci book. It has too many open ends. Maybe in 2 decades or so, then it will be interesting to tell how the stories developed.

Hi Zephir,

You again didn't get the point, so let me spell it out once more, though it's explicitly in the paper: the point is to look for quantum gravitational effects and ideally learn from that about the underlying theory. For that, one needs phenomenological models: Terra incognita is vast. Somebody gotta tell the experimentalists where to look. Your "criticism" is totally off target. Best,

Well, getting back to Phenomenology, that great blend between Experimental Physics and Theoretical Physics, I am grateful you work it, and work it hard, Bee. It's very discouraging to see the two groups split into "camps", but very encouraging to see YOU call "Bullshit!" and force the issues back on track.

It takes a woman to raise a village, so to speak. :-)

And yes of course it would make a good book. Look how FEW books on the subject are out there? Three books by Lee Smolin, Musser's and Jones' books, and Penrose if you dig enough. Oh, and a bazillion books about Superstring Theory that ignore the competition, the damned elitists.

As far as knowing more in 20 years, sure. What are we supposed to do, though? Wait until the LHC bangs out unexpected results and therefore MORE Experimental grist for the Theoretical mill? OK, but hasn't that always been the case.

If you're worried that your book will be outdated the day it hits the press, so what? Aren't they all? Then again, maybe you're right. But maybe not too, because you have this blog for updates, Works for Peter Woit, why not for you?

Thanks, that's very useful! I'll fix these sentences in an update. Strings aren't more likely to get caught in black holes than other stuff. Two of us are doing fine and are happily kicking what constitutes their food and oxygen supply, while the latter has to cope with an increasing amount of complications and is meanwhile on medication and bedrest. Lots of time to read all these papers I've piled up... Best,

/* Somebody gotta tell the experimentalists where to look */But theorists are apparently even more confused, then the experimentalists. It's evident on every discussion, which I've with You here. The point is, most of things, which theorists predicted are observable easily, but because theorists don't know about it, they cannot tell the experimentalists about it. We can say, theorists are living in different multiverse, then the experimentalists. For example:

Such ignorance has no better explanation, then just generating dummy jobs both for experimentalists, both for theorists. Contemporary physics is an industry with its own rules (which are separated from the needs of society) and based on selfinforcing principles, which are keeping it in motion.

Hi Bee,It seems like a good map of where physicists today are looking for answers. I have several critiques that may or may not be useful. I hope they will be. I don't want to appear to be just making catcalls from the peanut gallery. Also, it's very clear you put a lot of work into this.

You talked about trying to make a mix of top down and bottom up thinking. I still think there is too much bottom up thinking and not enough top down thinking from first principles. I see a lot of evidence in this paper of catering to every attendee's pet theory. I'm sure it is pretty much an impssible task to tell someone to their face that what they have been working on for the past ten years looks to you like a jury rigged monstrosity. I sympathize, but that's what a lot of these ideas look like to me.

The other thing is that except for the cosmic strings idea everything else in the paper concentrated on the high energy domain. In retrospect it seems kind of harsh all the critical comments you got here when you talked about cosmic strings. I think everyone focused way too much on the word "string". I think much more emphasis should have gone into the low temperature domain and tie it in directly with the evolving temperature of the cmb. There was hardly more than one or two mentions of the cmb and none at all that what is eft of what people call the Zero Point Field IS the cmb..

So it seems the actual question you're asking is: Why aren't the experimentalists interested listening to YOU in particular? Yeah, I wonder why. Regarding the points you mention, you already brought them up in this post one week ago, and I explained there that you're suffering from multiple misunderstandings. You didn't bother to do as much as thank me for spending time on trying to help you. Instead, you ignored everything I said, and now you're just repeating the same nonsense. Your attitude of ignoring criticism already clearly documents you're not a serious scientists. Still wondering why nobody is even remotely interested in listening to you? My recommendations is start listening to what people tell you. And, since you've probably forgotten about it again, let me repeat for the umpteenth time that this is *not* the place to discuss your own theory of something or other. Best,

Yes, I would agree with you. A phenomenological model you expect to be only approximately right and still leave open questions and possibly inconsistencies. Just that these issues should be in parameter ranges neatly separated from where you use the model. Ie, such that you could understand it as an approximation that doesn't make sense beyond some range. That's for example my big issue with DSR. It's not so much that I dislike it because it lacks a derivation or it's unclear (at least to me) what its motivation is. No, the problem is that the model has open questions and conflicts with the standard model (multi-particle states, locality) in parameter ranges that we have observation already. That's a big problem. On the other hand, you might ask questions like, what happens to the black hole/big-bang singularity in the quantum graphity model? Well, I have no clue, I don't know if anybody has, and I'm not even sure that's a meaningful question. But it's also not something that's an immediate problem. Best,

Regarding your first point. Well. Let me put it this way: There's things you can't write in a paper. As I mentioned somewhere, I was putting forward an agnostic view on these proposals for the purpose of giving the reader an impression. Seems you got the right impression ;-)

Regarding the second point, that's not true actually. There's several possible CMB signatures that I've discussed, these are generally in the low-energy regime (though that's probably a matter of perspective. They are low-energy today). There's also the Kaon-interferometry, and the Eötvös-like experiment. I should also add that there's was section that finally didn't make it into the paper, that of testing the foundations of quantum mechanics. Thing is, first, I was running out of space, and second, I was 6 weeks past the deadline already, and this section would have taken me a lot of time to write because I only have a very spotty knowledge about it. One thing that would fall into this category for example would be the recent experiments for testing the gravitational force on a BEC (if I recall that correctly), and similar things that make it into the category high-precision rather than high-energy. Best,

/*..you're suffering from multiple misunderstandings.. you didn't bother .. you ignored everything I said... you're just repeating the same nonsense... your attitude ... clearly documents ... you're not a serious scientists ... still wondering ...you've probably forgotten about it again...*/

It's symptomatic, when people are facing problems, they become focused to people, who are reporting them - not on the problems itself. Look Bee, I gave you a clear questions, which aren't EVEN REMOTELY related to my person - so I consider your reply completely OT in this extent.

I replied to your "questions" already in the earlier thread as I just told you. (It's not so much questions as actual statements of the sort "dark matter filaments are cosmic strings" or "there's a gravitational wave signature in the CMB noise." etc) I don't have the time to repeat myself endlessly, so do your homework. Further comments of yours that are not about the topic of this post will be deleted. Best,

After my initial reading of your paper I tend to agree with Steven, that it represents as being an excellent outline for a book on the subject, how about calling it “The Roads to Quantum Gravity; Including its Forks, Intersections, Bottlenecks & Dead Ends”:-) More seriously, whatever one might call it, such a book could prove to be useful on two fronts.

First it would give the young who are aspired to join the hunt a better idea what they are getting into and second as to offer the interested sector of the general public first hand insight as to where theoretical physics is headed, why it is headed there, the many challenges it faces and yet most importantly what being the reasons to understand that real headway stands to be made and the promise it brings.

One thing being certain, if you were to write such a book, it would be from the perspective of one that knows and has followed the path(s), yet most importantly one who in doing so having found reason why such as journey should be considered as generally worthwhile and important; not just to those few who continue the search, yet to all of us whenever terra incognita is changed to becoming terra firma.

”To date we have no experimental signature for quantum gravitational effects. But, as we have seen in the previous sections, creativity, persistence and technological improvements have brought us closer to this goal. The quest for quantum gravity may proceed slowly and sometimes be frustrating, but the reward will be nothing less than a revolution of our understanding of space and time.”

I would a agree in principle with Steve and Phil, yet insofar that you entitle this "chapter 1." :)

Any scientist has to arrive at syntactical views in order to leave the boundaries of their experience, or, they could be adding more data without really having concertize the parameters of their thinking?:)

After a while Eric, you get a sense of the slight of hand sarcasm toward methods of discovery in regard to views of early cosmos understanding that seem so far from phenomenological artifacts, after the fact?:)

But up to page eight and taking it slowly.:)

Cutting to the chase.

High energy plasmas? Given we understand the limitation LHC provides and how much more the universe has as a pallet of experiential conduct, we know we have garnered ourselves to a legitimate "point of view?":)

Dr. H comments: "The quest for quantum gravity may proceed slowly and sometimes be frustrating, but the reward will be nothing less than a revolution of our understanding of space and time.”---------------------------

I trust that you will agree that when one cannot even identify "experimental signatures", and consequently any immediate hope for definitive predictions, one needs to exercise quite a bit of humility.

What if the key to quantum gravity involves ideas that you summarily dismiss, like the fractal approach to nature and its discrete scaling for gravitation?--------------------------R.I.P. Benoit B. Mandelbrot; you showed us an amazing new paradigm for nature, which we have yet to fully appreciate.

With all due respect, but if I were expecting twins, with a lot of busy times ahead (not a couple of days or months, but very busy *years*), including a complete change in lifestyle, priorities, etc, I would not waste an erg with Zephir. There must be n copies of Zephir out there; only one of them really said good-bye. The others seem not to understand all that has been previously stated by you.

*Do* rest now, otherwise you will regret every bit of useless time/energy spent now. Unless you will have 24 h/day 7 days/week professionals or parents with plenty of time to help you, *do* take my advice seriously!

I do hope your hypothesis is proven wrong, as it could stand to be a major blow to both Darwinian Theory and Quantum Mechanics. That is it would be hard to understand how this could transpire by way of either a process of natural selection or one dictated by probability. None the less I do agree that Bee, more than most, should be mindful of the laws conservation, as to take the lagrangian approach more seriously in such respect.

Wegener proposed that the continents floated somewhat like icebergs in water. Wegener also noted that the continents move up and down to maintain equilibrium in a process called isostasy.Alfred Wegener

Okay,

In concert with phenomenological approach, how is this to be categorized in direction of Quantum Gravity research? In relation too, Eöt-Wash Group?

Dvali says. "Virtual gravitons exploit every possible route between the objects, and the leakage opens up a huge number of multidimensional detours, which bring about a change in the law of gravity."

Dvali adds that the impact of modified gravity is able to be tested by experiments other than the large distance cosmological observations. One example is the Lunar Laser Ranging experiment that monitors the lunar orbit with an extraordinary precision by shooting the lasers to the moon and detecting the reflected beam. The beam is reflected by retro-reflecting mirrors originally placed on the lunar surface by the astronauts of the Apollo 11 mission.What! Superficiality has extra dimensions to it?

So how does one manufacture consistent view of cosmos while we use Lagrangian approach as to how we see the universe in let's say a "gravitational approach?"

Is this consistent with perspective about how we look at the universe now becomes a focus toward quantum gravity research in legitimate process? Helps to set up focus toward Planck era and curvature?

You change the format from the very small to the very large just as you would recognize LHC limitations and the higher energy value for experimental search limitations. Eöt-Wash Group has found it's limitation?

Please don’t get too excited yet about rumors concerning the Eot-Wash test of the 1/r^2 law. We can exclude gravitational strength (|alpha|=1) Yukawa violations of the 1/r^2 law for lambda>80 microns at 95% confidence. It is true that we are seeing an anomaly at shorter length scales but we have to show first that the anomaly is not some experimental artifact. Then, if it holds up, we have to check if the anomaly is due to new fundamental physics or to some subtle electromagnetic effect that penetrates our conducting shield. We are now checking for experimental artifacts by making a small change to our apparatus that causes a big change in the Newtonian signal but should have essentially no effect on a short-range anomaly. Then we will replace our molybdenum detector ring with an aluminum one. This will reduce any signal from interactions coupled to mass, but will have little effect on subtle electromagnetic backgrounds. These experiments are tricky and measure very small forces. It takes time to get them right. We will not be able to say anything definite about the anomaly for several months at least.

The angular movements needed to signal the presence of additional dimensions are incredibly small — just a millionth of a degree. In February, Adelberger and Heckel reported that they could find no evidence for extra dimensions over length scales down to 0.2 millimetres (ref. 11). But the quest goes on. The researchers are now designing an improved instrument to probe the existence of extra dimensions below 0.1 mm. Other physicists, such as John Price of the University of Colorado and Aharon Kapitulnik of Stanford University in California, are attempting to measure the gravitational influence on small test masses of tiny oscillating levers.A matter of some gravity

Thank you for that link, Arun, Dick Lipton has a wonderful blog. I liked this comment:

Gilbert Bernstein permalinkOctober 20, 2010 6:28 pm

I’m sure you must have heard this terrible math joke, but just in case someone hasn’t. (I first heard this joke in a talk by Ron Graham. Credit where credit is due.)

Did you know that all numbers are interesting? What’s that? You don’t believe me? Well I have a proof. Suppose not every number is interesting. Then let n be the smallest uninteresting number. That’s a rather interesting property isn’t it?

I think the most valuable things being not those which we pass onto our children, yet rather those things we endeavour to have first preserved and then strengthened in them, being something which all children seem to be born with and that being a natural curiosity. That is I’ve found this being consistent with discovering as to what to be in common with the most creative of adults is they never truly grow up.

In “From Eternity to Here” I was surprised to learn that one of the measurable differences predicted by General Relativity is illustrated in this scenario.Say one builds a very tall tower up to the altitude of the orbit of a satellite and places a clock, one each, on both the tower top and the satellite. Apparently the clock on the tower would run more slowly because it is being accelerated upward by the tower and the one on the satellite is in under no net acceleration. Strange, yes, but I may get over it. With all the usual apologies for perhaps hopelessly naive questions, I am wondering if the acceleration provided by the tower is measurably quantized. Multiple regards.

The world's most precise atomic clocks are now made from "atomic fountains". A gas of atoms within a vacuum chamber is trapped by a set of intersecting laser beams and cooled to a temperature close to absolute zero. The ball of atoms is then tossed vertically into the air by changing the frequency of the lasers and it passes through a microwave cavity on its way up and also on its way down as it falls under gravity. The whole process is then repeated.Are the laws of nature changing with time?

If thinking had not been parametrized, then such questions "could not" have ever been poised?:)

Children, or no children?:)Yet, it would seem, that such a process might be construed as a birthing process?:)

....Since the 1930s physicists have discussed whether the constants that appear in the equations for the fundamental laws of physics--such as the speed of light in vacuum and the electron charge--are actually constant. If they have changed over time, nature may have worked in different ways at different times, even if the equations themselves have remained fixed. Modern theories that attempt to unify gravity with the other fundamental forces leave room for such a time-dependence. But it's not easy to look for the effect. If the speed of light were slowly decreasing, for example, we might never know it, because our measuring apparatus might be shrinking at the same time.....

Such assumptions, can have a drastic outlook/effect on all that we believed was sacrosanct?

So to seal it into a firm conviction one would of course accept an phenomenological approach to any speculation. To leave from that point, one becomes poised you see:)

Does one ever understand their motivations in the choice of this subject?

What drives your interest may and may not most certainly be driven by the same motivations of another, does not mean you discount that process to certainty?

S-Band Transponder Doppler Gravity Experiment

The gravity experiment used measurements of perturbations in the motion of the spacecraft to infer the lunar gravity field. Clementine was equipped with an S-band microwave transponder and 2 S-band omni-directional high-rate antennas which were used for tracking by the NRL tracking station in Pomonkey, MD, and the NASA Deep Space Network. The frequency of the S-band transmission was measured every 10 sec, and the Doppler shift would give the relative velocity of the spacecraft towards or away from the Earth. Accelerations were calculated from changes in the velocity, and after accounting for the orbit, relative motions of Earth and moon, and Earth and solar gravity, these accelerations are converted to lunar gravity effects on the spacecraft. The calculated lunar gravity field can be used to model subsurface lunar structure. The Pomonkey station could measure the velocity to an accuracy of 3 mm/sec, while the Deep Space Network stations could achieve about 0.3 mm/sec. Tracking was not possible on most of the lunar far side (120° to 240° long, -45° to 45° lat), when the moon was between the spacecraft and the Earth. In all, over 361,000 observations were made, approximately 57,000 at less than 1000 km altitude. Clementine (1994)

In response I believe to Don Foster's comment:With all the usual apologies for perhaps hopelessly naive questions, I am wondering if the acceleration provided by the tower is measurably quantized.

In which case I think Bee you just won the BackReAction's Fewest-Words-With-Most-Content award of the day. I will attempt to answer in a bitmore detail, and you can beat your personal best (thus winning 1st AND 2nd place today), with a one-word answer to Am I correct?

Measurable is what this whole business is about, because the energy required to "prove" quantum gravity is so large, we have to do creative end-arounds since we currently lack the energy atm to conclusively "prove" if gravity comes in quanta. Oh, the large astronomical observatories do have the chance to prove it, but great care must be taken, for various reasons.

True to begin with there is nothing of significance measureable in Don’s setup, yet beyond that there are basic conceptual problems respective of the actions of gravity relative to time under GR and what role acceleration does or doesn’t play in it and also to that of relative motion (speed). For instance if the tower’s base sit on the equator and the top of it at the same altitude as say that of a satellite in a geosync orbit then clocks of the same construction would measure time exactly the same.

What you say is roughly correct. In this case however it's not a matter of energy. The reason why there's no quantization of gravity to be found in such an experiment is just that the gravitational field of the Earth is much too weak. Weak as it is, it's to excellent precision classical. One can measure the quantization of particles in the classical field, but this has nothing to do with quantum gravity, and takes somewhat more effort. We discussed such an experiment here. Best,

An interesting piece you pointed out to Steven standing as one that you wrote prior to me becoming a follower of this blog. It’s so interesting in fact it reminds me that I should look back on what you’ve written since its inception. If I have you point correctly, being although the experiment stands to deminstrate that the motion of the neutrons is quantilized within a gravitation field it however is not able to have decided if the gravitational field being the same.

Thank you Bee, and Robert, of course the Philosophers (Natural, Professional and unfortunately Pop) "tipple" a bit as you put it? Where do you think the truly great ideas come from. ;-)

Again Bee, thanks, I see I have more to explore, and thanks for pointing the way.

Bee, what do you think of the latest from Fermilab re the MiniBooNE experiment as noted <a href="http://news.discovery.com/space/new-physics-discovered-by-miniboone.html>here</a>?

I'll note you've written many papers re neutrinos, and I'm confused. I want to believe we've found a fourth family of neutrinos, because it <i>may</i> mean we can put Dark Matter to bed thanks and work on the real sex, which is Dark Energy.

But I'm not sure, and I hate not kmowing stuff. My increasingly skeptical views of anything written in the press regarding the "next best thing" du jour leads me to question if there is truly anything there, or merely hype promoted by a person trying to keep his job. I've been disappointed this way more than once in the 2 tears since I converted back to Math and Physics, the two most base (therefore coolest) fields of study.

I wrote exactly one paper on neutrinos... I think at present it's likely, though not entirely settled, that something funny is going on regarding the difference in the neutrino/anti-neutrino oscillation pattern, but I think it's far from clear the right explanation is a 4th neutrino. It is also to some extend not "pretty" in that the additional neutrinos would have to be sterile. In any case, it's something to keep an eye on. Best,